1G Dreaded 2nd gear pop out..how to?

[CrackedDSM]

Hey guys, I’ve got the dreaded 2nd gear pop out issue. It partially grinds 2nd and if I don’t hold it firmly into 2nd for a second it’ll pop out.

I’m sure it’s the synchro, but how do I fix this?

Bigger question, do I need to change shims if I put a new gear/synchro in it or can I just slap her in and go?

 

[jdxnc]

The synchros only slow down the gears to let them engage, this would be the engagement teeth on the gear, the slider or both. This would require a complete disassembly of the trans and clusters to repair. Once you replace any parts, it needs to reshimmed.

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There's also a ball and spring for each rail on the front of the case that help keep the forks in the proper place, I highly doubt it's the issue but they're behind the 3 14mm caps on the bearing plate on the front of the trans, you could open them up and make sure the spring isn't broken but again, this is not likely.

 

[CrackedDSM]

The synchros only slow down the gears to let them engage, this would be the engagement teeth on the gear, the slider or both. This would require a complete disassembly of the trans and clusters to repair. Once you replace any parts, it needs to reshimmed.

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There's also a ball and spring for each rail on the front of the case that help keep the forks in the proper place, I highly doubt it's the issue but they're behind the 3 14mm caps on the bearing plate on the front of the trans, you could open them up and make sure the spring isn't broken but again, this is not likely.

I was afraid of this. Shit. Guess I’m on the hunt for a whole spare trans.

Another question: what would I have to do in order to use this in my 90 transmission? Do I need the corresponding shaft it slides on to?

Might as well upgrade while I’m at it.

 

[pauleyman]

Another question: what would I have to do in order to use this in my 90 transmission? Do I need the corresponding shaft it slides on to?

Might as well upgrade while I’m at it.

90 intermediate shaft uses smaller needle bearings under 1 and 2. You can't use a 93 up 2nd gear. To do the least amount if work you need a 91 intermediate. Its the only one that is both larger shaft as all 91 up are, but retains the different involute 3rd gear on only 90 91.

 

[CrackedDSM]

90 intermediate shaft uses smaller needle bearings under 1 and 2. You can't use a 93 up 2nd gear. To do the least amount if work you need a 91 intermediate. Its the only one that is both larger shaft as all 91 up are, but retains the different involute 3rd gear on only 90 91.

So jacks sells a 91 intermediate shaft. That’s what I’d need?

 

[pauleyman]

If you want to retain the 90 3rd and center diff, yes. 92 up uses a different 3rd gear involute gear pitch. Although 90 and 91 center diffs are internally different they are interchangeable as a unit. I built this exact Frankenstein 15 years ago

 

[jdxnc]

Although 90 and 91 center diffs are internally different they are interchangeable as a unit. I built this exact Frankenstein 15 years ago

Are you sure about the 91? 90 has a different gear pitch than pretty much anything else from my experience and can't be interchanged with anything else for the most part.

 

[CrackedDSM]

Why’d I have to have a 90 transmission. Lol.


Can I ask a really big favor. If I wanted to overhaul the trans can someone make a list? You don’t have to give me part numbers or anything just something like

1 - 2nd Gear and Synchro
1 - Hub/Slider
1 - 91 intermediate shaft


Etc. I’d like to fix this problem and also basically make it a brand new transmission.

 

[luv2rallye]

You might enjoy this: http://www.vfaq.com/mods/Trannyrebuild.html

 

[CrackedDSM]

You might enjoy this: http://www.vfaq.com/mods/Trannyrebuild.html

I actually downloaded that page and a few YouTube videos. Lol. I’m determined.

 

[pauleyman]

Are you sure about the 91? 90 has a different gear pitch than pretty much anything else from my experience and can't be interchanged with anything else for the most part.

Now you're making me second guess......
As I remember 91 intermediate is a 1 year only part. It is dimensionally the same as 92 up with the exception of 3rd gear pitch. @twicks69 you wanna chime in here?

 

[twicks69]

2nd gear popout typically occurs from a few issues, including:
*Excessively worn intermediate shaft tapered roller bearings causing bearing endplay and shaft movement.
*Excessively worn 1st/2nd hub and slider engagement teeth (chipped off engagement teeth, or totally flatspotted)
*Excessively worn 1st/2nd shift fork wear pads (you would see wear marks on the middle portion of the fork on whichever side is worn out. You can also measure the pad thickness vs the slider groove width to see how much free play the fork has on the slider.
*Synchro worn beyond its limits.
*Synchro friction surface flat spotted and glazed, causing it to not act as a brake to slow down the gear.
*Synchro cone on gear (if single synchro gear) heated / glazed / warped / out of spec.
*Gear engagement teeth to synchro / slider are excessively worn down, chipped, flat spotted. Gear requires replacement.

As for gearset compatibility, the details above are a little incorrect. There are several variations of gearsets, in this circumstance regarding 1990 gearsets vs 1991, etc, here are some important details:
*Gearset
------ 1989-1990.5 - "Early 90" style gearset regarding the gear profile for intermediate shaft, 3rd gear, 4th gear, center diff housing.
----------------> This style is the "Early 90" style, which has smaller needle bearing bores on the 1st and 2nd gears, using MD718033 small diameter needle bearings that are the same size as the 3rd needle bearing.
----------------> This small diameter intermediate shaft also uses a specific small diameter 1st/2nd hub for the hub and slider.
----------------> The "Early 90 and Late 90" style gearsets use the same 3rd/4th gears which have no markings on 3rd and 2 markings on 4th gear teeth as identifiers. Make note that the "90" style 3rd gear subgear IS DIFFERENT than the 1991.6-1999 style, or Evo 1-3 style profile and are NOT INTERCHANGEABLE!
----------------> This gearset uses the 2-hole 3rd/4th style shift fork.
----------------> This gearset uses the "90" style center differential housing without any external identifier markings on the housing gear teeth. It also uses a specific lower pinion oiling washer that has two "wings" to lock into the center differential housing. Since these lower pinion oiling shims are all obsolete, you can actually use stacked front differential pinion shims to get the desired thickness for pinion height / backlash internally. This is how we also do it on the PPG center diff housing when setting it up. For some reason PPG decided to use a 90 style pinion oiling washer that went obsolete.
----------------> This gearset uses the small diameter 5th/Reverse hub and slider assembly/synchros/ aluminum 5th/Reverse shift fork as well.
----------------> This gearset uses the "90" style shift rails and matching shift selector tab that have to stay as a matched set to work together.
------ 1990.6-1991.5 - "Late 90" style gearset regarding the gear profile for intermediate shaft, 3rd gear, 4th gear, center diff housing.
----------------> This is the "Late 90" style, which has the larger needle bearing bores on 1st and 2nd gears, using the MD737652 large diameter needle bearings and later version MD749414 hub and slider (1991-1999 style).
----------------> The "Early 90 and Late 90" style gearsets use the same 3rd/4th gears which have no markings on 3rd and 2 markings on 4th gear teeth as identifiers. Make note that the "90" style 3rd gear subgear IS DIFFERENT than the 1991.6-1999 style, or Evo 1-3 style profile and are NOT INTERCHANGEABLE!
----------------> This gearset uses the 2-hole 3rd/4th style shift fork.
----------------> This gearset can use 1990.6-1999 style 1st or 2nd gears as they all have the matching needle bearing bore size.
----------------> This gearset uses the "90" style center differential housing without any external identifier markings on the housing gear teeth. It uses a specific lower pinion oiling washer that has 1 tang on the underside of the washer with the same design as the 1990.6-1999 style differential housings to lock into the center differential housing.
----------------> This gearset uses the small diameter 5th/Reverse hub and slider assembly/synchros/ aluminum 5th/Reverse shift fork as well.
----------------> This gearset uses the "90" style shift rails and matching shift selector tab that have to stay as a matched set to work together.
------ 1991.6-1992.5 - "91-92" style gearset regarding the gear profile for intermediate shaft, 3rd gear, 4th gear, center diff housing.
----------------> This is the "91-92" style, which has the larger needle bearing bores on 1st and 2nd gears, just like the 1990.6-1991.5 as well as the later years 1992.6-1999 style components using the MD737652 large diameter needle bearings and later version MD749414 hub and slider (1991-1999 style).
----------------> The "91-92 style" gearsets use the same 3rd/4th hub and slider design as the "Early 90 and Late 90" style gearsets but now they have different profile intermediate shaft and 3rd/4th gears which have 3 markings on 3rd and 3 markings on 4th gear teeth as identifiers while using the small diameter 3rd/4th synchros.
----------------> This gearset uses the 2-hole 3rd/4th style shift fork.
----------------> This gearset can use 1990.6-1999 style 1st or 2nd gears as they all have the matching needle bearing bore size.
----------------> This gearset uses the "91-99" style center differential housing with one identifier marking on the housing gear teeth. It uses a specific lower pinion oiling washer that has 1 tang on the underside of the washer with the same design as the 1990.6-1999 style differential housings to lock into the center differential housing.
----------------> This gearset uses the large diameter 5th/Reverse hub and slider assembly/synchros/ steel 5th/Reverse shift fork as well.

I can go into further detail regarding 1992.6-1994 vs 1995-1996 vs 1997-1999 style gearsets but in this circumstance it is not needed to add.

 

[bastarddsm]

My vote is that it is thrust wear on the hub, or like Tim said smoked fork, or bearings. Either way trans needs a full rebuild. Expect to spend $2k, and wait 6+ months. If you buy a used one, plan on rebuilding it as well. About 9/10 "good working" used transmissions need full rebuild.

 

[pauleyman]

Tim I knew of the early and late 90 intermediate shaft as you mentioned but I always thought the late one was model year 91. Its been 15 years since I built a Frankenstein 90. Thanks for the information.

 

[CrackedDSM]

I’ll buy a spare trans and just save pennies to get someone to rebuild it for me. I think this is beyond what I’m willing to do tbh.

I’d really like a four spider upgrade too.